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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5189_Библиотеки_им_академика_М_И_Перельмана.pdf
Atrial Size andFunction
TahaAhmed, AmitArbune, andVincentL.Sorrell
14
Learning Objectives
1. Discuss how the left atrium is a critically
important modulator of left ventricular lling,
a volume sensor, and a barometer of diastolic
function.
2. Review optimal TTE techniques for assessing
LA structure and function.
Left Atrium
The left atrium (LA) is an oval-shaped structure
visualized posterior to the aortic root and superior to the left ventricle (LV) forming a large
part of the base of the heart. Anatomically, the
anterosuperior wall is adjacent to the ascending
aorta and pulmonary trunk and the posteroinferior wall is adjacent to the esophagus and typically has four pulmonary vein orices. The
posteroinferior wall corresponds to the diaphragmatic face; the mitral valve is positioned
at the anteroinferior wall; the medial wall corresponds to the interatrial septum and contains
Supplementary Information The online version contains supplementary material available at https://doi.
org/10.1007/978- 3- 031- 80038- 2_14.
T. Ahmed · A. Arbune · V. L. Sorrell (*)
University of Kentucky, Gill Heart and Vascular
Institute, Lexington, KY, USA
e-mail: Taha.Ahmed@uky.edu;
amitarbune@uky.edu; v.sorrell@uky.edu
the fossa ovalis; and the lateral wall contains the
left atrial appendage (LAA) [1]. The walls are
mostly composed of smooth muscle bers but
contain prominent trabeculae in and near the
LAA [1]. The atrioventricular orice is positioned lower anteriorly and is intimately related
to the mitral valve.
Imaging assessment of atrial size and function can be performed using cardiac computed
tomography (CCTA) and cardiovascular magnetic resonance (CMR); however, transthoracic
echocardiography (TTE) is conventionally the
initial diagnostic modality given its safety prole, portability, comprehensive capabilities
with high temporal and spatial resolution.
Complete assessment of the LA includes the
use of real- time two-dimensional (2D) and
three- dimensional (3D) TTE, Doppler techniques, and off-line analysis of quantitative volumes, function, and novel speckle-tracking
determination of mechanical properties [2].
Although not exploited in clinical practice,
TTE is well suited to provide a detailed assessment of LA structure and function.
The LA functions as a reservoir draining from
the pulmonary veins during ventricular systole, a
conduit during early diastole, and a contractile
pump during late diastole to complete left ven-
tricular lling just prior to the LV contraction and
mitral valve closure [2]. An alteration in the LA
dimension and function may impact any one of
these three components of the LA function.
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2025
M. J. Lanspa, A. T. Levinson (eds.), Echocardiography and Ultrasonography in the ICU,
Respiratory Medicine, https://doi.org/10.1007/978-3-031-80038-2_14
181
182
T. Ahmed et al.
Left Atrial Size, Dimensions,
andVolumes
Left atrial (LA) size quantication is complicated
by the complex LA geometry, intricate ber orientation, and the variable contributions of the left
atrial appendage and pulmonary veins. LA volume determination is one of the rare circumstances
in which TTE is preferred over transesophageal
echocardiogram (TEE) due to the intimate esophageal/LA relationship that limits visualization in
the immediate near-eld [2].
Due to the challenges of securing an accurate
scan plane and the variable patterns of LV dilation, linear dimensions using M-mode or 2D-TTE
have been replaced by estimation of LA volumes
from visualization in multiple views [3].
Utilizing apical two- and four-chamber views
in orthogonal planes to the left atrial long axis,
phasic measurements of the LA are performed
(Figs.14.1 and 14.2). Carefully tracing the maximally visualized border of the LA in two orthogonal views allows you to apply the ultrasound
system’s biplane Simpson’s method of disc formula to determine the LA volume (LAV)
(Fig.14.3).
Once calculated, the LAV is indexed to the
body surface area (LAVI) to correct for changes
related to physical stature and categorized by
sex (Table 14.1) [2]. Importantly, given the
current ubiquitous prevalence of obesity in
society, the normal relationship of LAV to BSA
is altered and the optimal method to index the
LAV is being scrutinized [4]. To better understand this relationship, the maximal (LAVI
and minimal (LAVI
) are being carefully
min
max
)
investigated and matched to clinical outcomes.
The LAVI
is strongly associated with pre-
max
dicting cardiovascular outcomes. However, its
prognostic value is lower in atrial brillation
(AF) [2]. Recent ndings suggest that LAV
min
is more strongly associated with AF than
LAV
regardless of using isometric or allo-
max
metric height-indexation [5].
Call Out
In a retrospective assessment of >300
patients in sinus rhythm, LAVI
measured
max
in the biplane 2-D apical views was found
superior to four-chamber LA area alone or
LA dimension in predicting the development of rst atrial brillation (AF), congestive heart failure (CHF), cerebrovascular
accident, acute myocardial infarction, coronary revascularization, and cardiovascular death over a 3.5-year follow-up [6].
Fig. 14.1 LV four-chamber and two-chamber views with long axis along the LV where LA is not well visualized
14 Atrial Size andFunction
Fig. 14.2 Dedicated LA views in four-chamber and two-chamber orientation demonstrating better visualization of the
LA and foreshortening of the LA
183
Fig. 14.3 Biplane measurement of the LA volumes in the four-chamber and two-chamber views on dedicated LA
views
Table 14.1
tions for cardiac chamber quantication by echocardiography in adults: an update from the American Society of
Echocardiography and the European Association of
Cardiovascular Imaging [2]
LAVI Males and females
Normal (mL/m
Mild (mL/m
Moderate (mL/m
Severe (mL/m
LA size gradation as per the recommenda-
2
) <34
2
) 34–41
2
) 42–48
2
) >48
• Apical TTE images dedicated to the LA chamber should be obtained to avoid LA foreshortening that may occur with conventional
LV-aligned apical TTE images.
• The lengths of the LA measured in the two
orthogonal views should be similar (e.g.,
within 5.0mm) and provide a quality measure
to minimize foreshortening.
• While tracing LA borders, the conuences of
the pulmonary veins and the LAA should be
excluded.
Technical Considerations
• The atrioventricular interface should be represented by the mitral annulus plane, not by the
While assessing the LA using TTE, the following
tip of mitral leaets.
technical considerations are vital [2, 3]:
• LA size should be measured when the chamber is at its greatest dimension (typically,
end-systolic).
184
Call Out
A systematic underestimation of 2DEacquired LAVI
compared to CCT and
max
CMR is observed, likely due to foreshortening and difcult endocardial border visualization.
Where CCT and CMR have their own
limitations, real-time 3DE is gaining popularity as the modality of choice to accurately measure cardiac chamber volumes
with lower interobserver variability and
higher test-retest reproducibility compared
with 2DE [7].
LAVI is a predictor of the development of
heart failure and poor clinical outcomes, irre-
T. Ahmed et al.
spective of LV systolic function. In patients
with heart failure with preserved ejection fraction (HFpEF), the relevance of LAVI is perhaps even greater. Although normative data
and prognostic utility of 3DE are warranted,
evaluation of LA parameters will likely be
included in future guidelines (Figs.14.4 and
14.5, Video 14.1).
Evolving Evidence
There is recent evidence suggesting that
LAVI
may be a more important prognos-
min
tic indicator using either 2DE or 3DE [8].
Current recommendations encourage the
reporting of the maximum and minimum
LAVI.
Fig. 14.4 3D-TTE, apical four-chamber, two-chamber, and short-axis views providing the volumetric assessment of
the LA size and function. The bottom lines represent the time-volume curves for LA physiology
14 Atrial Size andFunction
185
Fig. 14.5 3D-TTE captured as a full volume loop, showing the apical four-chamber, three-chamber, and twochamber views for the LV and volumetric rendering of both
LV and LA along the LA and LV volume curves at the bot-
Summary Points
• LA chamber dimensions often dilate asymmet-
rically with the disease, should be measured
using biplane LAVI, and 3DE is superior to
2DE and allows the determination of LAVI
and LAVI
which may offer additional prog-
min
max
nostic value compared with LAVI alone.
• Accurate LAVI determination requires careful
acquisition is confounded in AF and mitral
valve disease and is underutilized in routine
clinical practice.
Left Atrial Function
Left atrial function holds signicance and can be
assessed using conventional 2D and Doppler techniques, as well as more contemporary 3D volumetric and speckle-tracking deformation analysis.
A volumetric assessment of LA function can
aid in assessing total, passive, and active emptying
(ejection) fractions, representative of the reservoir,
conduit, and booster pump function, respectively.
Doppler waveforms of pulmonary venous
ow (LA lling) and trans-mitral ow (LA emptying) can be used to estimate relative atrial func-
tom calculated on the Philips EPIQ machine utilizing the
Heart Model A.I. 3D tool. The tool calculates the LA volumes, LAVI, and LAEF as well. This eliminates the need
for dedicated LA views for accurately obtaining LAVI
tions. The ratios of peak trans-mitral early (E)
and late (A) velocities (or their velocity time integrals [VTIs]) and the atrial lling fraction (A
[E
+A
VTI
atrial booster pump function. The ratio of systolic
]) estimate the relative contribution of
VTI
(S) to diastolic (D) pulmonary venous ow estimates relative reservoir to conduit function
(Fig.14.6). The magnitude and duration of pulmonary vein ow reversal during atrial contraction (PVa) are used to estimate atrial contractility
and LV diastolic pressure [9]. Atrial ejection
force is the force exerted by LA to accelerate
blood into LV and is, yet another Doppler parameter studied for atrial systolic function [6].
Call Out
Interpretations of pulsed wave spectral
Doppler indices are challenging in patients
with sinus tachycardia, conduction system
disease, and arrhythmia (especially AF),
and obtaining high-quality pulmonary
venous recordings may be difcult. A disadvantage of spectral Doppler is its lack of
specicity [6].
VTI
/
186
T. Ahmed et al.
Fig. 14.6 2D TEE, mid-esophageal window,
48-degree display of the pulsed wave spectral Doppler
analysis with the sample volume positioned in the left
superior pulmonary vein demonstrating the LA
Deformation analysis utilizing atrial strain
and strain rates (SR) representing the magnitude
and rate, respectively, of myocardial deformation
have been applied in an effort to better understand left atrial mechanics. This was initially
assessed using tissue Doppler velocities (TDI)
but has more recently been evaluated with 2D
speckle-tracking echocardiography (STE) techniques (Fig. 14.7). STE analyzes myocardial
motion through frame-by-frame tracking of natural acoustic speckles, from interactions between
ultrasound and myocardial tissue, within a userdened region [6]. Frame rates of approximately
50–70 frames/s are needed to prevent speckle
decorrelation, and good image quality is crucial
for accurate tracking.
An LA-focused apical four-chamber view is
recommended to generate longitudinal strain and
strain rate curves throughout the cardiac cycle out
of which regional and average values can be cal-
phases—S corresponding with the reservoir (blue
contour), D corresponding with conduit (green contour) and PVa (yellow contour) corresponding with
LA pump function
culated [6]. The myocardial region of interest is
dened by the inner and outer LA wall contours.
The tracing should start at the endocardial border
of the mitral annulus with extrapolation of the
contour across the pulmonary veins and the LAA
orices. Global longitudinal strain is dened as
strain in the direction tangential to the endocar-
dial atrial border in the apical view [6].
The left atrial appendage is rarely optimal
using TTE and therefore TEE is considered
standard to assess emptying velocities and assess
for the presence of thrombus (Fig.14.8).
2D strain and strain rate imaging overcome
much of the subjectivity and variability inherent
in assessing endocardial motion. A recent small
report suggests that LA reservoir strain can be
reproducibly measured with a standardized methodology which incorporates self-directed education [10]. However, these methods fail to address
the complexities of 3D cardiac geometry and
14 Atrial Size andFunction
Fig. 14.7 2D apical four-chamber view demonstrating 2D LA strain measurement
187
Fig. 14.8 2D TEE orthogonal 95- and 51-degree
imaging planes from the mid-esophageal window
demonstrating pulsed wave spectral Doppler velocities of the LAA.LAA exit velocities in a patient with
motion. Data suggest that 3D speckle-tracking
echocardiography (3D STE) overcomes these
limitations because it eliminates the effects of
through-plane motion that may occur with 2D
imaging [11]. By design, one can measure longitudinal and circumferential strains from a single
3D dataset. Moreover, the evaluation of LA endocardial area strain is possible. To date, this is not
available in clinical practice.
organized atrial flutter (>40cm/s) are seen on the left,
and abnormal LAA exit velocities in a patient with
sinus rhythm, but low flow (<20cm/s) are seen on the
right panel
Another very important consideration in the
assessment of LA size and function is recognizing the differences associated with aging
where it is known that the LA dilates despite
normal aging and a compensatory rise in
booster function, which serves to compensate
for the age- associated changes in LV function,
is expected [12].
188
Evolving Evidence
Normal values for 3D STE are available
but are limited in the number of patients
studied. Although time and expertise in
analyzing 3D LA datasets have raised concerns, advancements in articial intelligence with automated analysis can
potentially resolve these issues.
Caveats inSick Patients
Recognition of LA structural and functional
abnormalities is essential in critically ill patients.
In response to stressors such as diastolic dysfunction (DD), tachycardia, ischemia, and valvular
disease, the LA adapts to a spectrum of complex
structural changes, often referred to as “LA
remodeling.”
In a prospective cohort study, the LAVI was
found to be the best predictor of MACE and
prognosis [13]. In ischemic heart disease and MI,
an exponential increase in mortality in patients’
post-MI is observed with increasing LAVI
[14]. Another study showed a LAVI
>32mL/m
max
[2] to be an independent predictor of 5-year mortality [15]. More recently, the ASE guidelines for
LAVI upper limits of normal were increased from
28 to 34mL/m [2] for added specicity and a better risk-based cutoff [2].
In patients with systolic heart failure, a
LAVI
>50mL/m [2] showed a similar predic-
max
tive value as LVEF <45%. Unarguably, an
enlarged LA is a marker for both the severity and
chronicity of LV DD and the magnitude of LA
pressure elevation. A graded response of LAVI is
observed as the severity of DD increases and
evaluating LAVI is key in evaluating DD in current guidelines [16]. However, an important
caveat is that it cannot be used in AF or signicant MV disease.
In a multicenter study of >350 patients, an LA
strain (LAS) value of >23% was considered normal, when this cutoff was applied to patients with
DD, interestingly reduced LAS was observed in
patients with normal volumetric measures, indicating strain to be more sensitive marker of DD [17].
max
T. Ahmed et al.
In patients with diastolic heart failure, one
study showed LA strain to correlate with wedge
pressure and provided a discriminatory value
between HFrEF, HFpEF, and DD [18]. In a
Korean study of 300 patients with paroxysmal
AF evaluated longitudinally, an LA global strain
of <30.9% was associated with a fourfold risk of
permanent AF [19]. Another study in AF patients
showed global LAS provided incremental value
when added to CHA2DS2VASC score, presence of
OAC, and LA volumetric function in separating
patients at risk of developing and mortality from
embolic stroke [20]. Moreover, in AF, LAS has
been shown to predict the maintenance of sinus
rhythm after cardioversion and pulmonary vein
isolation [21, 22].
In patients with severe mitral regurgitation
undergoing MV surgery, LAS is found to be a
more powerful predictor of adverse outcomes
even compared to left ventricular strain [23].
In critically ill COVID-19 patients, acutely
reduced LA function has been observed with a
signicantly reduced LAS associated with AF
development [24]. In orthotropic heart transplantation recipients, a signicant correlation is found
between LA and RA size (and donor and recipient remnants) and overall survival [25].
Summary Points
LA function can be accessed via multiple parameters and has particular use in patients with
HFpEF. It is more sensitive than LA volume
change and holds prognostic value. LA function
assessment requires training and expertise, there
is vendor variability with no standardized normal
values and for the past 15years and to date, still
we use an LV algorithm for LA strain assessment.
Atrial Septum
Abnormalities of the interatrial septum include a
patent foramen ovale (PFO), atrial septal defect
(ASD), and atrial septum aneurysm (ASA). PFO
is prevalent in 25–30% of the population and
results in the probability of intermittent bidirectional ow between the atria [26]. An atrial septum that is hypermobile and protrudes >1.0cm
14 Atrial Size andFunction
189
rightward or leftward or >1.5cm bidirectionally,
is considered an ASA [27]. An ASA is usually
seen with 2D TTE, commonly associated with a
PFO, and can be more precisely interrogated with
TEE.A thorough assessment of the atrial septum
can be performed with the aid of contrast echocardiography, color Doppler imaging, or both.
The ability to visualize right-to-left (R-L) shunting is dependent on interatrial pressure gradients
which can be provoked by physiologic parameters (e.g., Valsalva release) [26]. During an agitated saline echocardiographic bubble study, an
R-L shunt is typically observed within three to
four cardiac cycles from when bubbles are rst
seen in the RA. However, a better method to
assess for a PFO would be to more temporally
search for R-L shunting associated with transient
atrial septal leftward deviation which would conrm an R>L interatrial pressure gradient [28].
Fatty inltration of the atrial septum, mostly in
the superior and inferior portions is called lipomatous hypertrophy, giving the septum a dumbbellshaped appearance since the fossa ovalis (in the
center of this dumbbell) is never involved.
Right Atrium
embryologic remnant of the valve directing IVC
blood across the interatrial septum. Lack of the
normal regression of the Eustachian valve may
lead to partial or complete septation of the RA,
inappropriately labeled as cor triatriatum dexter
[30]. It can be best visualized on a parasternal
long-axis view at the junction of IVC and
RA.Although often xed and immobile, it can be
mobile and confused for a pathologic cardiac
mass, or even an atrial septal defect.
A Chiari network (CN) is another embryologic remnant that is typically seen as multiple filamentous linear structures within the
RA and located near the orifice of IVC.The
CN is highly mobile and may be confused as a
pathologic mass (e.g., vegetation or thrombi)
[31].
The IVC is best visualized from subcostal
views and compliance-related changes in the
dimensions of IVC help estimate the RA pressure. Increased end-expiratory IVC diameter,
measured proximal to the RA junction, can be
secondary to the volume overload state.
Furthermore, a blunted or absent respiratory variation in the IVC diameter>50% is an excellent
estimate of increased RA pressure [29, 32].
The Right Atrium (RA) receives deoxygenated
blood from the superior and inferior vena cava
(IVC) as well as the coronary sinus. It is a thinwalled ovoid structure. A dilated and diseased
RA frequently accompanies right ventricular volume and pressure overload. RA size and function
are less well studied compared to the LA.For RA
size assessment on TTE, apical-four chamber or
subcostal views are utilized at the end-systole,
measuring the RA area and RA volume index
similar to LA for enhanced accuracy [29].
Visually enlarged RA compared to LA in apical
four-chamber view is qualitative evidence of
chamber enlargement. The RA can be at risk of
compression by mediastinal or herniating abdominal structures, e.g., the liver. Distinguishing
extra cardiac compression from intracardiac
masses may at times be difcult.
Certain anatomic variants within the RA
require consideration. The Eustachian valve is an
Call Out
Doppler assessment of right atrial lling is
important, especially in critically ill
patients. On a subcostal view, alignment of
the Doppler beam with IVC ow is difcult,
hence while utilizing hepatic vein ow as a
surrogate due to better alignment of
Doppler signal, diagnostics for various
causes of elevated right atrial pressure such
as severe tricuspid regurgitation, atrial
brillation, restrictive cardiomyopathy, and
pericardial constriction can be made [32].
Summary Points
• LAVI
measured in the biplane 2-D apical
max
views is superior to four-chamber LA area
alone or LA dimension in predicting the
development of rst atrial brillation, conges-
tive heart failure, cerebrovascular accident,
190
T. Ahmed et al.
acute myocardial infarction, coronary revascularization, and cardiovascular death.
• A systematic underestimation of 2DEacquired LAVI
compared to CCT and CMR
max
is observed and is likely due to foreshortening
or poor endocardial border visualization.
• Real-time 3DE is gaining popularity as the
modality of choice to accurately measure cardiac chamber volumes with lower interobserver variability and higher test-retest
reproducibility compared with 2DE.
• There is recent evidence suggesting that
LAVI
may be a more important prognostic
min
indicator using either 2DE or 3DE and current
recommendations encourage the reporting of
both the maximum and minimum LAVI.
• LA chamber dimensions often dilate asymmetrically with disease reiterating the importance of volume measures over dimensions.
• Accurate LAVI determination requires careful
image acquisition to reduce foreshortening.
• Normal values for LA mechanics using STE
are available but limited by the number of
patients studied.
• Advancements in articial intelligence with
automated LA strain analysis packages continue to evolve and will likely become standard care in the future.
• LA function holds particular value in patients
with HFpEF and is more sensitive than LA
volume change for predicting outcomes, but
requires training and expertise and there are
limited standardizations.
• Doppler assessment of right atrial lling patterns is important when assessing critically ill
patients.
• Hepatic vein ow is used as a surrogate marker
for IVC ow due to better alignment of the
Doppler cursor and offers important diagnostic estimates of right atrial pressure, severity
of tricuspid regurgitation, and has unique
spectral waveforms in patients with either
restrictive cardiomyopathies or pericardial
constriction.
Questions
1. What is the recommended optimal method for
assessing the size of the left atrium with
echocardiography?
A. Visual estimation from dedicated apical
four-chamber and two-chamber views
B. Linear diameter of the LA from M-mode
on the parasternal long-axis view
C. Linear diameter of the LA from M-mode
on the parasternal short-axis view
D. Tracing the LA on dedicated transthoracic
apical four-chamber and two-chamber
views
E. Tracing the LA on mid-esophageal TEE
apical four-chamber and two-chamber
views
Answer: D
The best way of estimating the LA size is
by tracing the LA borders in two orthogonal
views, the LA-focused apical four- and twochamber views, and estimating the volume
using the Simpson’s method of disc. Option e
is incorrect since TEE will rarely completely
visualize the entire LA and commonly underestimates true dimensions. If the dedicated
LA focus views are not obtained, the LA
dimensions can be inaccurate since the LV
long-axis view may foreshorten the LA [4].
2. Which of the following supports a diagnosis
of intrapulmonary shunting on a 2D-TTE agitated saline bubble study?
A. Early appearance of the saline bubbles in
the LA and LV within three cardiac cycles
B. Early appearance of the saline bubbles in
the LV, but not the LA
C. Early appearance of the saline bubbles in
the LA or LV after Valsalva maneuver
D. Late appearance of the saline bubbles in
the LA or LV after ve cardiac cycles
E. Late appearance of the saline bubbles in
the RA or RV after ve cardiac cycles
Answer: D
Saline contrast study or bubble study can
be used on a TTE or TEE to differentiate